Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
20579~7
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01METHOD ~ND APPARATUS FOR BROADE3AND E~ECTRO~IAG1~15TIC
02ENERGY COUP~NG
03
04FIELD OF TE~E ~NVENTION
_
OS
06 The present invention relates g~nerally to th~
07 electromagnetic coupling and analy~l~. More ~peci~ically,
08 thls invention provide~ an antenna which can co~bine th~
og function~ of various resistivity and ~ielectrlc con~tant
device~ into a single tool, capabl~ of operating ov~r a wide
11 range of frequencies. It i~ particularly u~eful i~ the
12 field of medical technology.
13
14 BACKGROUND OF TH~ ~NV~NTSON
16 In the field of medical technology, lt i~ well knon~ that
17 electromagnetic en~rgy i~ u~eful ~n variou~ type~ of
18 dlagno~es and treatments. For example, recent ~ta~irtic~
19 show that pulmonary and cardiopulmonary di~ea~es ar~
re~ponsibl- for more than three ~ on ho~p~tal a~ isfiion~
21 and 30,000 death~ every year in the United States.
22 Pulmonary abnor~litieA are virtually alway~ as~oc1~eed w~th
23 change~ ln lunq w~ter content or distributlon. Mo~t workers
24 agre~ that the~ no single, nond~tructiv~ ~ctbod
availablo to detoct accurately early change~ in lung
26 water content.
27
28 For a elinlcally u~eful techniquo, it 18 deslrabl~ to detect
early ch~nge~ ~n both thc extr~vascular lung wat-r, which
~trongly r~flect~ mo~t pul~onary abnor~alitie~, and the
31 intravascula~ compartment. Recently, the U80 of the
32 electromagnetic ~ethods to detect changes in lung ~ter
33 content have shown promi~ing initial result~, particularly
34 for detecting small variat~ons in water content.
2 ~ 7
01 Particularly at microwave frequencies, changes in the
02 dielectric properties of tissue are closely related to the
03 amount of water present. Electromagnetic techniques,
04 therefore, basically utilize changQs in th~ permittivity and
oS conductivity of the lung region to detect change~ in lung
06 water content. This method has the advantag~ of u~ing
07 highly penetrating electromaqnetic signals rather than
08 ultrasonic signals which are both highly attenuated and
og di~pcr~d in the lung. Furthermore, electro~agn~tic
techn~ques hav~ the potential or continuous monitoring of
11 patients in intensive care units, such as those ~ith heart
12 failurc or extensive burns.
13
14 U.S. Patent No. 4,240,445 issued to ~skand~r et al. and i6
incorporated hereln by re~erence for all purposes. Iskander
16 teache~ a method of coupling electrom~gnetio ~norgy into a
17 material such a~ tissue, to mea~uro water content.
18 Measuring lung water content is an especially u6eful
19 application. ~owever, I~kander'8 device i~ ~o lasge that
only a few antenna~ can b~ place on th~ che~t, and the
21 ant0nna cannot be de~cribed a6 a po1~t ~ource. Also, the
22 electrie f~ld vanishe~ at some di~tanc~ fro~ th~ ~ntenna,
23 as the electric field~ ln th~ t~o parallol -~lots are
2~ oppositely dir~ct~d. Furth~r~ore, ~ res~tor is included in
the antenna, which d$ssipate4 much of the el~ctro~agnetic
26 energy ln the antenna itself and introduce~ a limitation in
27 th~ power handling capability of th~ ant~nna. Additional
2~ pr~or wor~ includess M. F. Iskander and C. H. Durney
29 (1980): "Electro~gnet$c Technigue~ for Medlcal Diagno~is:
A Reviewn, Proceeding~ of ~EEE, vol. 68, no. 1. and
31 M. F. Iskander et al ~1982): nTwo-dimensional Technique to
32 Calculate the EM Power Deposition Pattern in tho Buaan
33 ~odyn, Journal of Microwave Power, vol. 1~, no. 3. There is
34 thus a need for a device that is compact enough to permit
~3~7
01 placing of many antennas forming an array on a ches~ to
02 obtain a well-defined image of the chest cavity, a device
03 that has an antenna that can be mathematically de~cribed as
04 a point source, and one which does not suffer fro~
05 cancellation of the electric field at a certain distance.
06
07 A dielectric transm$tting and mea~uring devic~ can also be
08 used to heat an interior portion o~ a mammalian body to
og de~troy or reduce the size of tumors. Tumor reduction
therapy, or cancer therapy by hyperth~rmia, co~bined with
11 radiation or drugs is known in the art to either stop or
12 slow down the growth o cancer cells, or cau~e the death of
13 the cancer cells. (Se~, for example, Streff~r, C., ~Cancer
14 Therapy by Hyperther~ia and Radiation", Urban and
Schwarzenberg, Munich, F.~.G., 1980 and Detbylefs~n, L.A.
16 (Edltor), "The Thlrd International Sy~posium: Cancer
17 Therapy by Hypcrthermia, Drugs and Radlation, Colorado State
18 University, Ft. Collin~, U.S.A., 1980.)
19
one such devic~ i~ disclo~ed by J. Scheiblich ~t al.
21 "R~iofreguency-Induced Hyperthermla in the Pro~taten,
22 Journal of Mlcrowav~ Power, vol. 17, no. 3, 1982, Otta~a,
23 Canada. Sche$blich et al's d~vice wor~ only at
24 singl~ fr~quency.
26 ~ propagating ~loctromagnetic wave ha~ two fund~ental
27 charactori~tic~, a~plitud- and phase. ~y comparing the
28 amplitudo and pha~e of an electromagnctic wave aE it passes
29 receivers, propag~tion characteri~tics of the probed ~edium
may be studied, Measurem~nt of these two charactetistics
31 may b~ used to deter~ine th~ dielectric con~tant and
32 the conductivity of th~ media through which the waY~
33 ~8 propag~ted.
34
2 ~ 4 7
01 However, no one tool in the prior art is capable of probing
02 or coupling energy into a material over a broad b~nd of
03 frequencies. It is therefore advantageou~ to exten~ the
04 frequency range.
05
06 ~he largest hurdle to developing such a broadband dielectric
07 tool has been the lack of a suitable broadband antenna that
08 can couple electromagnetic energy to and fro~ ~ material,
09 and that i8 compact enough to fit within the oonf$nes o~
a tool.
11
12 ~ho prior work i5 limited in the atte~pt~ at electromagnetic
13 coupling, analysis, and treat~ent, in that no suitable
14 c~ngle antenna elemont has been designed which can couple
electrom~gnetic energy into a material, suzh as na~mal
16 tissue, over a broad range of frequencie~, that i~ also
17 suficiently compact and is capablè of handling high power
18 levels. There i8 therefore a need for a d~vice and a method
19 for use in such broadband applicat~ons.
21 SVMMARY OF 'rHE ~NVENI'ION
22
23 The present invent$on 18 6urprislngly ~uccessful in
24 providing a method and apparatus for co~bining the functions
o~ v~riou~ conductivity and dielectric constant device~ and
26 electro~agnetic energy coupling device~ into ~ single
27 devica, capable of oporating over a w~d~ rang~ of
2~ frequenci~. It is especially useful in medlcal
29 technology applicatlon~.
31 A measuring or electro~agnetic coupling tool, having a tool
32 face, also has a nov~l transmitting an~enna and a novel
33 rece~v~ny antenna~ Electro~agnetio energy i~ trans~itted to
34 a transmitting antenna. A stripline adapter permit6 the
r
2~7~7
01 energy to flow to a striplins having a metallic central
02 strip. A strip face of the central strip is bent at
03 approximately right angles, and has a height that is
04 compatible with desired frequency coverage.
05
06 A ground plane extends ~rom the stripline adapter to the
07 right angle bend, so that a distal end of the central strip
08 extend~ away from it, and a void is created between the
09 center strip and the ground plane.
11 A dielectric is positioned to nearly fill the void. The
12 dielectric is comprised of a material h~ving a very high
13 dielectric constant and a very low energy lo~. The
14 transmitting antenna is positioned 30 that the ground plane
15 i8 fixedly connected to the measuring tool, ~nd the strip
16 face lies flu6h with th~ tool face, so that electromagnetic
17 energy can be transmitted into the material to be analyzed.
18
19 An enclosure surroundlng the strlpline i8 compr~sed of four
metallic walls which ar~ po~itioned ln electrical contact
21 with the ground plane and the 6tripline adapter, so that the
22 strlp fac~ i5 ne~rly c~ntered in the open~ng created by the
23 walls znd the ground plane.
24
A loss-les~, non-conduct~ng material fllls in any remaining
26 open ~pa~ in-the enclosure, so that the non-conductinq
27 materi~l form~ an add~tional wall that i8 really flat with
~8 the strip face.
29
3~ A receiving antenn~ i8 co~prised in essentially the same
31 manner a~ the transaitting antenna, and is position~d in the
3a tool 80 that it can re~eive the electromagnetic energy which
33 has traveled through the ma~erial being probed. A means for
34
2~7~7
01 monitoring the received energy detects the phase and
02 the amplitude.
03
04 In another embodiment of this invention, broadband
05 measurements are taken to determine the quanti~y of a fluid
06 in a material, such as water in a lung.
07
08 It le one object of thi~ invention that electro~agnetic
og energy ls trans~itted and received over a w$de frequency
range, specifically from a few KHz to a few G~z. A commonly
Il used frequency range is fro~ 2 R~z to 4 GHz.
12
13 The tool may further comprise a pad, which ~u~3tantially
14 conforms to thc surfac~ of the ma~l tls~u~, and hold~ the
antennas. At lea~t one tranEmitting antenna i~ n~ce~sary.
16 No receiving antenna i8 n~cessary, although a plurality of
17 each 1~ often d~sirable.
18
19 The above and other embodiments, ob~ects, advantages, and
zO features of the lnventlon will become mor~ r~adlly
21 apparent f~o~ th~ following detailed de~oriptlon of the
22 invention, which i~ provided in conn~ctlon with the
~3 accompanying drawing~.
24
D~:SCRIPTION OF THE DRAW~NGS
216
27 Flgure 1 1~ a ~ch~tic, ~ectional vi~w of thc inventlve
28 deviec po3~tioned ad~acent to mammal ti sue.
29
Figure 2 show~ a top, front, and side view of the novel
31 trans~itting antenna.
32
33 Figure 2A is the sa~e view as Figure 2, further illustrating
34 ~he enclosing ~etalllc walla.
2 ~ ~ 7 ~ 4 7
01 Figure 3 shows an antenna mounted on a tool face.
02
03 Figure 4 shows three graphs of transmission and return loss
04 as a function of frequency.
05
06 Figure S i8 a graph of transmission and return lsss as a
07 function of frequency, for low frequencies.
08
09 Figure 6 shows four graphs of ttme-dom~in tran~ission
measurements at various distance fro~ a ~etal reflector
11 plate ln a brine.
12
~ 3 DETA~ED D~:SCRIPTION O~ THE ~NVISNT~ON
14
In accordance with the present invention, a neu l~proved
16 method and apparDtus for coupllng electro~agnetic ~n~rgy
17 into a material for determining the nature of various
18 materials and the fluids contained there~n and to induce
19 hyperthermia, u~ing a broadband ~easuring apparatus, has
been developed.
21
22 Referrlng to the drawings, a fir~t ~bodi~nt of th~
23 in~entlve broadband tool 101 i8 ~hown ln r~gur~ 1,
24 position~d around a portion of a ~am~al body ~uch a~ a chest
cav~ty 103. A m~an8 such as a belt moun~ 109 po~itions tool
26 faoe 111 n~ar th~ ma~l skin 104, such that tr~n~mitt~ng
27 antanna~ ~uch as Tl and T2 and receivin~ ant~nna~ ~uch as Rl
28 and R2 are po~ltioned touching the skin sur~ace of 104. The
29 tool fac~ lll is de~ined as the surfa~ of the b~lt
mount 109 contaln~ng ~he ap~rture plan~ of the antennas, and
31 is preferably a continuou~ metall~c surface. The belt
32 mount 109 may b~ mado of any suitabl~ flexible ~at~rial that
33 ean be ctrapped around the portion of in~ere~t o~ the ~ammal
34
01 body. A conducting compound such a~ a conducting grease may
02 be applied at the interface 113 bet~een th~ tool face 111
03 and the skin surface 104 to improve coupli~g betwe~n the
04 antennas and the che~t cavity 103.
05
06 The region of the mam~l body to be inve~tigated ~ay not be
07 electrically homogeneous. In the ch~t oav~ty 103 for
08 example, there are organ~ such as th~ heart 105, th~ lung
09 region 106, the vQrtebra 107, and ther- ~y also b~ ~
10 tu~or 108. It i~ often deslrable to ~nalyz~ or treat
11 selected portions of suoh a cavity 103.
12
13 An analysis of the chest cavity 103, for exa~ple, can be
14 done by a dielcctric lmaging of tb~ c~vity. Thi~ i 8 don~ by
transmltting electromagn~t$c energy at a ~ult~ble freguency
16 across th~ che~t cavity 103 froo a tran~-itting antenna such
17 as ~1, and receiving this energy ~t a r~c~iving antenna such
18 as Rn. In this way the phas~ and tbe amplitude of the
19 propagated electromagnetic w~ve for th~ path TlRn (shown in
da~hed line) is deter~lned. Since ther~ ca~ b~ a
21 multiplicity of tran~mitting antenna~ Tn and a multiplicity
22 of rccelving ~ntenn~ Rn, ~ ~ultipl~clty of ~uch paths
23 crisscrossing the entire che~t cavity can b~ ~tudl~d. From
2~ this information, using well known t~chniq~e~, a dislectric
image of th~ ch~t cavity can b~ generat~d. Such an image
26 display~ th~ v~riou3 organs in the ca~ity, and wb~n ~uitably
27 made, can r~vcal th~ presenco of tu~or loa. The dl~lectric
28 propertie~, and thus a dielectric i~age, can be deter~lned
29 as a function of po~ition within the ma~erial being probed.
Since diel~ctric i~agc is very s2ns~tive to tho pre~ence of
31 water, it can al80 give an a sess~ent of th~ lung water
32 content; C~. nMicrowavc Methods of Mea~uring Change~ ln Lung
33 Water~, by M. F. I~kander and C. H. Durney, Journa} of
34 Microwave Power, vol. 1~(3), 1983, p. 265.
2~7~7
01 Note that althouqh the antennas have been labeled as either
02 transmitting or receiving antennas, any given antenna can
03 serve either function.
04
05 The broadband capability of th~ antennas is an ~dvaneage in
06 the above applications for the following rea~on~:
07 structures (e.g., heart, tu~or) of different size~ require
08 different frequencie~ for their best definition in th~
og image; highly lossy region~ such as fluids ~y reguire
employment of relatively low freguencies so that th~
11 electromagnetic losses are acceptable; in ti~e-do~in
12 application, simultaneous inform~tion at a ~ultiplic~ty
13 f frequencies can be developed.
14
In the trestment mode, it is desirable to reduce o~
16 ellmin~t~ the tumor 108 by hyperther~la, i.e., by
17 selectively heating only the tumor region 108 to a high
18 temporature. ~hus, by selecting a suitable group o~
19 antennas to tr~nsmit, one can select~vely deposit
electromagnetic energy in the reglon of th~ tu~o~ 1~8; Cf.
21 "Two-dimensicnal Technique to Calculate th~ E~ Po~er
22 Deposition Pattern in tho Humnn Body~, by M. F. i~zder,
23 P. F. Turner, J. B. Du80w and J. Rao, Journal o~ Micro~av~
24 Pow~r, v~l. 17(3), 19~2, p. 175.
~5
26 The broadband capability of the antenna~ ~ 5 ~n advantag~ in
27 the abov~ application because for a given situ~tion, one c~n
2B select the fr~gu~ncy that simultaneou~ly produco~ th~
29 optimum depo~ition of power and localization of th~ beating
using known technlques.
31
32 An exa~ple of the inventive trans~itting antenna 15~ is
33 shown in Figure 2. A coaxial connectin~ means, such as
34
~7~7
--10--
01 coaxial connector 151 is electrically conneeted to a
02 stripline adapter 153 which is capable of transmitting
03 electromagnetic energy from the coaxial connector 151 to a
04 stripline section with metall~c central strip 155. An
05 especially useful stripline adapter is a model No.
06 3070-1404-lD designed by Omni-Sp~ctra, or other types of
07 microwave stripline adapters. Other types of tran~is~ion
08 means may be utilized to transmit electromagnetic energy to
09 the antenna. For example, a strip transmisslon line may be
electrically connected to the stripline section having the
11 metallic central strip 155. As a com~ercial
12 coaxial-to-stripl~ne transition means has been utilized, the
13 d$menslons included herein reflect thi~ mean~. One
14 knowledgeable in the art would realize that the
dimens~ons ~ay be altered to change frequency coverag~
16 and to fine-tune performance.
17
18 Metallic center strip 155 has a front end 157, a flat strip
19 body 159, a flat strip face 161, and a distal end 163. The
front end 1~7 18 electrically connected to the e~ter
21 conductor 169 of the striplin~ adapter 153. Solder i~ a
22 particularly useful connecting means. Flat strlp body 159
23 may al~o be tapered to eom0 to a point at front ~nd 157 to
24 provido a s~ooth electrical tran~$tlon betw~en th~ center
conductor 169 and the center strip 155. Th~ strlp face 161
26 i8 b~nt at app~oximately right angl~s to strip body 159, and
27 ha~ a helght that i~ mea~ured from the right angle bend to
28 di~ta~ end 163. The height is compatible with th~ desired
29 frequency cover~ge. The longer the helght, the ~ore lower
frequ¢ncy coverag~ is allowed. A ~" height permit~ a
31 frequency rang~ of approximately 2 KHz ~ 1 GHz. A Sm~
32 he$ght extends the upper frequency limit to approximately
33 2 GHz. An upward frequency limit of 4 GHz is attainable as
34
~7~3~7
o1 well. The metailic center strip 15S can be made of any
02 metal. Copper, brass, or aluminum are especially useful.
03
, 04 A ground plane 165 extends fro~ stripline adapter 153 to the
right angle bend in the center strip 155, so that the distal
06 end 163 extends away from the ground plane 165 and so that a
07 void exists between the center strip lSS and the ground
08 plane 165. Ground plane 165 ls comprised o~ a ~etal.
Commerclal grade stainle s steel ls particularly useful. ~t
is desirable to keep the ground plane and center ~tr~p a~
11 short at pos~ible, to permlt the appar~tus to re~ain a~
12 compact as po~sible and to allow the use of a~ many antennas
13 as possible.
14
lS The vold between the ~round plane 165 and th~ center
16 str$p 155 ~8 largely f$11ed wlth a dielectric 167. The
17 dielectr~c 167 should have a very h1gh dielectric constant
18 and a very low 1055. 3y loss, w~ mean the dissipation of
19 energy. The dlelectric 167 can be a cera~ic di~lectric, and
comprised of mat~r~al such as ~ariu~ Tltanate or ~ad
21 2irconate T~tanate. A cryst~lline dielectric may also be
22 used, although ~ore exp~ns~v~. The thicknes~ of th~
23 dlelectrlc 167 i~ deter~ln~d by th~ ~tr~pl~n~ ~d~pter 153
24 used. The d~electric 167 acts to m~k~ the c~paeltanc~ of
the center str~p 155 very large.
26
27 The conat~uction o~ th~ antennA i5 comploted by ~nclosing
2~ the cent~r strlp 155 by met~llic w~115 181, 182, 183, and
29 184, wh~ch contact the ground planc 165 and th~ adapter 153
electrically, as shown in Figure 2A. The walls add rlgidity
31 and prev~nt le~ag~ 3~ the electromagnetlc radiatio~. The
32 strip face 161 i8 approxi~ately cen~ered in the r~c~angular
33 opening created by the edge3 of the walls and the ~dge of
34 the ground plane 165. Thus, the dl~tance betwe~n an edge of
~ t7
-12-
01 the strip face 161 and the adjacent edge of a wall is
02 substantially the thickness of the d$electric 167. The
03 entire void space in the antenna enclosed by the walls,
04 including the set back 168 at the dielectric edge, is filled
05 with a loss-less, non-conducting material such as a mixture
06 f epoxy and alumina which sets hard, seals the antenna, and
07 makes it more rugged.
08
og The ground plane 165 and the walls 181, 182, 183, and 1~4
are fixedly connected to an electromagnetic coupling or
11 analyzing tool as seen in Figure 3. The strip face 161 is
12 positioned to lie flush with the tool face 171 (whlch is the
13 sa~e as the tool face 111 of Figure 1), so that the
14 transmitting antenn~ 150 can transmit electro~agnetic energy
into a material such as mammal tis~u~. A conductive
16 6ubstance, known in the art, i 8 usually placed on the
17 outside of the mammal ticsue, to permit a suff$cient flow of
18 eloctromagnetic en~rgy into the tlssu~. Void space 173 is
19 filled with a loss-less~ non-conducting m~terial such as an
epoxy-aluminum compound. The ground plane 165 and the walls
21 181, 182, and 1~3 connect to th~ tool fac~.
22
23 A receiving ele~tromagnetic antenna is comprised in
24 essentially the same manner as the transmittinq antenna, and
is positloned in th~ tool in th~ same manner as the
26 transmitting antenna, so that the receiving antenn~ can
27 receive the electromagnetic ener~y whlch has t~av~led
28 through the ~aterial that is analyzed.
29
The pre~ent invention is especially useful in the field of
31 microwave diagnostics of fluid conten~ and flu~d quantlty.
32 For example, the apparatus can coupl~ electromagnetic energy
33 into ~ammal tiSBUe. The electromagnetic energy can be
34 monitored to provide an indication sf th~ amount ~nd
2 ~ ~i 7 ~ ~ 7
-13-
01 distribution of a fluid, such as water, in~ide the mammal
02 tissue. One particularly useful applic~tion is to measure
0~ the water content in a lung. The present apparatus is very
04 compact, and therefore requlres a much smaller skin contact
05 area. AlSo, many antennas can be placed on a ehest cavity,
06 to obtain a well defined image of the chest cavity. The
inventive antennas can be ~athematlcally d~scribed as a
08 point source, thus making analysis of the data easier. A
0~ conductive 6ubstance should bc pl~ced on thc outsid~ of the
chest cavity, to permit a ~ufficient flow of electro~agnetic
11 energy into the chest cavity.
12
13 The prior art (Iskander et al.) has the drawbac~ that the
14 electric field vanishes ~t so~e distanc~ froa th~ tool face,
since the fields in the two parallel ~lots ar~ oppositely
16 directed. No such cancellation occurs with the present
17 invention. Furthermore, the incorporat~on of a resi tor in
18 Iskander et al's antenna introduces a powcr limit~tion.
19
In another embodiment, the pre~ent inventio~ ca~ be used in
21 the field of microwave hyperth~r~ia. Th~ ~pparatus can
22 couple electrom~gnetic energy into the interior portion of a
23 mammal, so th~t the electromagnetic energy i3 focu~ed to
24 he~t and thereby reduc~ the size of or destroy a tu~or.
Tumor reduction therapy or cancer therapy, by hyperthermia,
26 co~bined with radiation or drugs is known in the art to
27 eith~r stop or slow down the growth of cancer c~ , or
28 cau~ th~ de~th of the cancer cells.
2g
The present invention has the advan~age over the prior art
31 that many frequeneies can be selected. B~caus~ there is no
32 limitation to the power handling capability in the inventive
33 antenna, the present invention is particularly suited for
34 depositing microwave power into a locali~ed area inside a
.3 ~ 7
-14-
01 mammal, such as a human. Either a single antenna or an
02 array of antennas could be used.
03
04 In yet another embodiment, the apparatus can be iDplanted
05 inside the body of a mammal, and used as a radio frequen~y
06 antenna. Either a single antenna or an array of ~ntennas
07 could be used. As the inventive antenna c~n be ad~ very
08 small (as small as approxim~tely 10 m~ long and
09 approx~mately 5 mm high), it is particularly ~uitDbl~ to
this application. As the antenna get~ smaller, the
11 frequency coverase shifts to higher frequencles. The
12 apparatus can be constructed with a comm~rcial ~cro-coaxial
13 connector. However, smaller devices can be oonEtructed
14 through the use of a custo~ized coaxial connector~
16 The apparatus can operate in the frequency domain~ u~ing a
17 single frequency, multiple frequencies ~such as
18 simultaneous, selectable, or time-multiplex~d fo~ example~,
19 or swept frequency techniques. Or, th~ apparatu~ can
operate ln the time domain, usin~ pulse~ of a wid~ variety
21 of shapes, widths, rise and fall times, etc. Whe~ thc
22 pulses are transformed to the frequency do~ain, eit~er
23 electronically using a spectrum analyze~, oe nus~ric~lly
24 using mathe~atical ~ransfor~s, the sam~ infor~at~on i5
obtained as would be given by a frequency do~ai~ tool.
26
27 A prototypc tool was constructed, with the inventiv~
~8 antenn~s. The tool consists of one transmitting and one
2g receiving antenna, the distance between the~ bei~g variable.
31 An acceptable dielectric antenna ~ust meet the following
32 criteria:
33
34
2 ~ 1 7
-15-
01 (i~ It must be able to couple sufficient energy into
02 and from the material at its operating frequency
03 to allow probing of the material;
04
05 ~ii) This probing energy must penetrate into the
06 material, rather than clinging to the ~urface of
07 the tool (i.e., it must trav~l as a freely
08 propagating wave rather than a surface wave guided
09 along the tool face).
11 In the present instance, the above two conditions must hold
12 over the entire range of the frequency of op~rat~on.
13
14 The first of the above criter~a i8 ~ested by mea~uring the
return los~ for th~ tran6mltting antenna, and th*
16 transmi~slon 108s from the trans~ltting to the receiving
17 antenna - both a6 a function of frequency. These
18 measurements are shown in Figure 4 where the tool i8 placed
l9 in air and again~t br~ne of conductivity 0.5 mho/~ (to
rep~esent a biologioal medium). The return loss curve in
21 brine shows that sufficient energy is entering the brine
22 over the frequeacy r~nge of the measuring devic~
23 (Hewlett-Pack~rd HP~505A Network Analyzer; 500 K~z -
24 1300 MHZ) to pormit probing. The tran~$sslon logs ~hows
that sufficient energy i5 being received at the r~ceiving
26 antenna to permit measurements.
27
28 Measurements were made by using another ~easuring device
29 (~P3577~ Network Analyz~; SHZ - 200 MHz) to test the low
frequency li~lt~tion o the antenna. The re~ult~ are shown
31 in Figure 5, showing that the low frequency limitation is
32 a~out 5 KHz. The improved return loss performance in ~he
33 200 MHz region (a~ Figur~ 4) results fro~ a drylng tcuring)
34 of the epoxy alumina fil}ing between measur~ent~.
7 ~ ~ 7
-16-
01 Figure 6 shows time-domain transmission measurements at
02 various distances (d) to a metal reflector plate in the
03 brine. The change in amplitude of the received pulse as a
04 function of the distance of the metallic refleetor shows
05 that the energy has penetrated into the brine out ~o the
06 location of the plate.
07
oa While a preferred embodi~ent of the invention ha~ been
og described and illustrated, it ~hould be appar~nt th~t ~any
modification~ can be made thereto without dep~rting fro~ the
11 spirit or scope of the invention. Accordingly, the
12 invention is not li~ited by the foregoing de~cr~ptlon~ but
13 is only limited by the s~ope of the clai~s appended hereto.
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